Exploring Cellular Biomechanics at Calvarial Suture - A Soft-Hard Tissue Interface

骨细胞是骨中最丰富的细胞，是处理生物力学刺激和通过其广泛的腔隙-小管网络（LCN）调节重塑事件的控制中心。虽然控制骨细胞LCN排列的关键因素尚不清楚，但发现机械负荷能够交替细胞和网络拓扑结构。发现LCN的这些特征与细胞外基质（ECM）矿化密切相关，通过ECM矿化，纳米级矿物颗粒嵌入有机胶原基质中。矿物颗粒的不同数量、大小和排列通过骨骼的层次结构决定了骨材料的性质。反过来，这些ECM矿物条件会影响相应的重塑事件。连续效应物一直致力于理解长骨中生物力学载荷、LCN特征和ECM矿物质状况之间的相互作用，它们的相互作用被认为是骨质疏松症、骨关节炎和骨关节病等病理状况的指示性指标。与长骨中LCN特征和ECM矿物条件的新发现相比，对其他类型的骨骼（如颅骨）知之甚少。颅骨由纤维缝合线（夏普氏纤维）连接。这种软硬（缝线-骨）组织界面不仅在出生时提供颅骨灵活性，也是膜内骨生长的主要部位，以适应胚胎发育和出生后早期生长过程中神经颅骨的快速扩张。这些缝合线传递生物力学信号，平衡成骨细胞的增殖及其分化以形成新骨。有趣的是，缝合线必须保持开放不骨化，以维持其扩展颅骨骨前缘的功能。骨化导致缝合线过早闭合（颅缝闭锁）影响约1 / 2000的新生儿，并可导致面部和颅骨外观异常；严重时，会引起颅内压增高，导致视觉损伤、睡眠障碍、咀嚼功能障碍、智力发育受损，甚至猝死。另一个主要的临床挑战是骨瓣吸收和颅骨成形术失败后，影响婴儿和成人。研究机械刺激-细胞-矿物质相互作用可以为缝线形态发生和骨形成提供一些时间和空间上的见解，这可能有助于阐明涉及这些临床疾病的可能机制。本项目旨在回答以下两个密切相关的基本问题。1)缝合线中的纤维组织如何以3D方式连接颅骨，生物力学刺激如何在该组织界面上分布？2)作为主要生长部位，缝线对骨细胞LCN排列和ECM矿化的时空影响是什么，沿着缝线和远离缝线？为了回答这些问题，学生将被要求执行-微ct成像，共聚焦显微镜，反向散射成像-图像分割和分析-逆向工程建模-机械状态的有限元分析

As the most abundant cells in bone, osteocytes are the control centre to process biomechanical stimulus and to regulate remodelling events through their extensive Lacuno-Canaliculi Network (LCN). While the key factors governing the arrangement of osteocyte LCN remain unclear, mechanical loading is found capable of alternating cellular and network topology. These characteristics of LCN are found closely associated with extracellular matrix (ECM) mineralisation, through which nanoscopic mineral particles are embedded in organic collagen matrix. The different amounts, sizes, and arrangements of mineral particles contribute to bone material properties through a hierarchical structure in bone. In return, these ECM mineral conditions affect consequential remodelling events. Continuous effectors have been dedicated to understanding the interaction among biomechanical loading, LCN characteristics, and ECM mineral conditions in long bone, and their interaction is believed as indicative for pathological conditions, such as osteoporosis, osteoarthritis, and osteoarthrosis.Compared to the emerging findings of LCN characteristics and ECM mineral conditions in long bone, very little is yet known for other types of bone, such as in calvaria. The calvaria bones are joined by fibrous sutures (Sharpey's fibres). Not only providing the cranial flexibility during birth, this soft-hard (suture-bone) tissue interface is also the primary site of intramembranous bone growth to accommodate the rapid expansion of neurocranium through embryonic development and early postnatal growth. These sutures transmit biomechanical signals and balance the proliferation of osteogenic cells and their differentiation to form new bone. Interestingly, sutures must keep their patency from ossification to maintain their functionalities in extending calvaria bone fronts. Premature closure of sutures (craniosynostosis) by ossification affects approximately 1 out of 2000 newborns, and can lead to abnormal facial and cranial appearances; in the worse scenarios, it will cause the increased intracranial pressure leading to visual damage, sleeping disorder, masticatory malfunction, impaired mental development, and even sudden death. Another major clinical challenge is bone flap resorption and cranioplastic failure following decompressive craniectomy, affecting both infants and adults. Investigating into the mechanical stimulation-cell-mineral interaction can provide some temporal and spatial insights in suture morphogenesis and bone formation, which potentially helps elucidating possible mechanisms involving these clinical conditions.This project is structured to answer the following two closely related fundamental questions.1) How do fibrous tissues in sutures connect the calvaria bone in a 3D manner and how is the biomechanical stimulus distribution across this tissue interface?2) As the primary growth site, what are the spatial and temporal effects of a suture on osteocyte LCN arrangement and ECM mineralisation, along and further away from a suture?To answer these questions, the student will be required to perform -microCT imaging, confocal microscopy, back-scattered imaging-image segmentation and analysis-reverse engineering modelling-finite element analysis for mechanical status